The present disclosure relates to composite materials. In particular, embodiments herein relate to core-shell nanocomposites comprising mixed organic-inorganic components.
Organic/inorganic nanocomposites are materials made up of organic polymers embedded with inorganic nanoscale fillers. The benefit of combining inorganic nanofillers within organic polymers is that the resultant composite becomes more rigid, thermally stable and displays other unique properties not seen with organic polymers alone. The polymer itself confers processability to the composite and imparts flexibility, improves dielectric properties and is ductile. The nanofillers provide a significant increase in interfacial area which creates a significant volume fraction of interfacial polymer with properties different from the bulk polymer, even at low loadings. The physical properties of the inorganic nanoparticles, in particular, can be enhanced by encapsulating or embedding within a polymer.
There is a growing interest in embedding nanometals into polymer matrices due to the potential applications that are possible. By combining the properties from both inorganic (i.e., silver, gold, copper, etc.) and organic (polymer) systems, many new products can be created. Areas of growth with regard to silver nanoparticles (AgNPs) include, without limitation, antimicrobial applications, biosensor materials, composite fibers, cryogenic superconducting materials, cosmetic products, and electronic components. The unique properties (e.g., size and shape dependent optical, electrical, and magnetic properties) of silver nanoparticles, in particular, have resulted in their increased use in number of consumer and medical products. Methods such as three dimensional (3D) printing and ink jet deposition can be used to transfer the functional core-shell organic/inorganic nanocomposites disclosed herein to a substrate of choice. Other areas of application include, for example, aqueous ink formulations for sensor and antimicrobial applications.
Most methods for silver/polymer nanostructured materials require that the silver salt precursor is reduced in a chemical reaction prior to incorporation into polymer matrices. The most widely used silver ion precursor for the synthesis of AgNPs is silver nitrate (AgNO3). The most readily used reducing agents for the synthesis of AgNPs are sodium borohydride or sodium citrate. The most common stabilizing agents for nanosilver are citrate and PVP (polyvinylpyrrolidone).
Conventional methods for making silver/polymer nanostructured materials generally require the melt mixing or extrusion of AgNPs in polymer matrixes which lead to aggregated silver particles. Other methods use in situ synthesis of metal nanoparticles in polymer matrixes which involves the dissolution and reduction of metal salts/or simultaneously with polymer synthesis. The polymer matrix has a role in keeping the AgNPs dispersed as well as maintaining overall chemical and mechanical stability.
Methods for the synthesis of core-shell or hybrid colloid dispersions currently lack control of morphology and colloidal properties are generally inferior. It has also been found that most conventional methods require filtration, sedimentation, and centrifugation processes, which are challenging and time consuming. The development of processes for the synthesis of core-shell organic/inorganic nanoparticles with precise positioning of the silver nanoparticles at the surface of the nanoparticle, as disclosed herein, provides reactive or stimuli-responsive colloidal particles that also have a well-defined structure, homogeneous encapsulation and well-defined morphology. Other issues that arise in conventional methods which are overcome by the methods herein include incompatibility between the polymer and inorganic material especially when highly hydrophobic monomers are used in any polymerization stage of the process. In these cases surface modification or treatment of the inorganic nanoparticles are usually employed to make the nanoparticles compatible and thus dispersible within the organic polymer matrix.
Finally, it is known that uncoated silver nanoparticles can be toxic but when protected by an organic layer or embedded within an organic matrix they become less toxic or in other words biocompatible.